We now turn to the low density regime, \(|n|<n^*\) , and address the \(T\) -dependence of the minimum conductivity, \(\sigma _{min}\) . Figure 4 shows \(\sigma _{min}(T)/\sigma _{min}(5K)\)  in samples S1, S2 and S3 before and after annealing. Before annealing, \(\sigma _{min}(T)\)  varies only slightly from 5 K to 240 K (\(<30\%\) ). The variation is similar to \(\sigma _{min}(T)\)  in unsuspended samples of similar mobilities [1]}. This is in a sharp contrast to the current-annealed devices, where \(\sigma _{min}\)  acquires a strong \(T\) -dependence, as large as a factor of \(1.5-3\)  for \(T=5\)  K to 250 K. This confirms that the \(T\) -independence of \(\sigma _{min}\)  observed in low mobility samples [1]}, [3]} is not an intrinsic property of graphene.
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